It is a more powerful and, in the case of the earlier cars, a slightly longer version of the company's previous 4/4 model.

After World War II Morgan re-introduced their 4/4 model fitted with a 1267 cc Standard engine.

The Plus 4 at its introduction was fitted with a 2088 cc Standard Vanguard engine installed on a widened and strengthened 4/4 chassis with a wheelbase lengthened by 4 in (102 mm).

In 1953 a higher performance version was announced with the 1991 cc, 90 bhp (67 kW) straight-four engine as used in the Triumph TR2 (a development of the Vanguard motor).

Beginning in very late 1953, the radiator grille was now surrounded by a cowl that blended into the bonnet; initial cars received an interim version which only curved backwards at the top (nineteen examples were built of this design), followed by a transition version using the final cowled design which also curves backwards at the sides coupled with lower-mounted headlamps.

[1][2] The final design, with higher mounted headlight pods and the badge above the grille appeared sometime in 1954; flat radiator cars were frequently returned to the factory to have the front updated, along with various technical upgrades.

A 4-seater version of the drophead coupé was available in 1954–1956 only; due to the complexity of the build, Morgan lost money on every one of these cars (which can be recognized by having a regular boot with a lid) and the type was discontinued after 51 examples had left the factory gates.

[6] Following the success of the LawrenceTune modified example at Le Mans in 1962 a higher performance version, the Plus 4 Super Sports, was available from 1962 with a tuned engine and a "low-line" lightweight, aluminium body.

While some changes were necessary to gain European Type Approval, others were dictated by customers, such as the addition of a long-door variant in 1997.

Plus 4 highlights include: Chris Lawrence and Richard Shepherd-Barron won the 1601-2000cc GT class at the 1962 24 Hours of Le Mans driving a Plus Four.

The Competition model had a low-line steel body, similar to the Morgan "Super Sports" aluminum body, and generally came with a Derrington four branch exhaust manifold, Derrington competition steering wheel, 72-spoke wire wheels, Armstrong select-a-ride electrically adjustable rear shock absorbers, and the 2.2-litre twin SU carburetor TR4 engine.

The wealthy heiress and debutante who is the subject of the Frank Zappa song "Florentine Pogen" drives "a '59 Morgan."